Traditional types of electrical analog voltage or current measuring instruments are being replaced increasingly by various kinds of digital measuring instruments, including the dot or bar display instruments. In these, a series of light emitters are sequentially energized as the voltage or current monotonically varies. Thus, a moving mechanical pointer is replaced by a moving light.
Such displays employ a voltage divider having a plurality of successive tapping points which provide a corresponding series of successively different reference voltage levels. The unknown voltage to be indicated is compared in a series of comparators with the said successive different reference voltage levels to furnish a corresponding series of binary outputs indicating whether the unknown voltage is higher or lower than the respective reference voltage level. These binary outputs control the energization of respective light emitters.
In the past, it has been the practice to electrically energize the voltage divider by applying a controlled voltage to one end of the voltage divider while the other end is connected to ground. See, for example, the disclosures in the U.S. patents issued to Kugelmann et al, Nos. 3,987,392, Lazowski, 4,092,591, and Weber, 4,318,152.
Further, it is obvious that different voltages could be applied to the two ends of the voltage divider, rather than to connect one end to ground.
For example, the National Semiconductor Corporation's data sheet for their LM 3914 Dot/Bar Display Driver.COPYRGT.1981 states that "the internal 10-step divider is floating and can be referenced to a wide range of voltages" and includes an application example wherein the voltages applied to the ends of the internal 10-step voltage divider are 4.5 and 5.0 volts, giving an expanded range of 0.5 volts with a suppressed zero.